Connection device for a turbocharger, and turbocharger

ABSTRACT

A connection device for an exhaust gas turbocharger has an essentially bent first element and an essentially bent second element. The first element and the second element are detachably connected with each other in a first end region or in a second end region, respectively, and are movably connected with each other in a third end region or in a fourth end region, respectively. A first supporting portion extends between the first end region and the third end region and a second supporting portion extends between the second end region and the fourth end region. The connection device comprises a recess which is formed in the element for the reduction of stresses.

TECHNICAL FIELD

The invention relates to a connection device for an exhaust gas turbocharger and to an exhaust gas turbocharger.

BACKGROUND

An exhaust gas turbocharger suitably consists of several casing sections: A first casing section which is generally flown through by hot gases, normally by exhaust gas of a combustion engine, a second casing section which is configured to accommodate a rotor assembly which is rotatably supported in the second casing section and is positioned between the first casing section and a third casing section which may generally be flown through by ambient air. Flange surfaces are formed between the individual casing sections in such a manner that these flange surfaces are contacting each other so that the hot gas and the ambient air are prevented from escaping as far as possible. If leakages occur between the flange surfaces, the total efficiency of the exhaust gas turbocharger will be reduced, on the one hand, and, on the other hand, environmentally harmful exhaust gases will exit between the first casing section and the second casing section, which, in particular, has to be prevented. It has to be taken into consideration that the exhaust gas turbocharger should be able to be disassembled, i.e. that for example a material bond connection between the individual flange surfaces might provide tightness between the flange surfaces, however, the exhaust gas turbocharger may then no longer be able to be easily disassembled and reinstalled.

A connection between the first casing section which is flown through by exhaust gas and the second casing section which is flown through by air or lubricant and/or water is highly problematic, because here large temperature differences as well as temperature variations between the casing sections occur. This means that the connection device has to compensate for different thermal expansions of the casing sections and is itself subject to different and varying stresses.

The connection device is usually formed like a pipe clamp, wherein two elements extending over a circumference of the connection device are at their ends facing each other detachably connected at least on one side by means of a screw-nut connection.

From the laid open publication DE 10 2014 103 683 A1, for example, a profiled clamp may be taken, whose ends of the elements facing one another in the region of the screw-nut connection are provided with a nose each so that flange portions of the elements are preferably exclusively in contact with the noses. The elements are profiled and comprise flanks which are formed trapezoidal because the profiled clamp is intended for making a taper flange connection.

During operation of an exhaust gas turbocharger comprising the connection device, high tensile and compressive stresses occur at certain places of the connection device, usually in end regions of the essentially shell-shaped elements which are connected with each other. These tensile and compressive stresses may lead to elongations and, in the worst case, to failure by rupture during operation.

SUMMARY

The object of the present disclosure is to provide a connection device for an exhaust gas turbocharger which ensures a reliable connection. The additional object is the indication of an improved exhaust gas turbocharger.

This object is solved by a connection device for an exhaust gas turbocharger as described. The additional object is achieved by an exhaust gas turbocharger as described.

The disclosure relates to a connection device for an exhaust gas turbocharger with an essentially bent first element and an essentially bent second element. The first element and the second element are detachably connected with each other in a first end region and in a second end region, respectively, and are movably connected with each other in a third end region and in a fourth end region, respectively, and wherein a first supporting portion extends between the first end region and the third end region and a second supporting portion extends between the second end region and the fourth end region, wherein the supporting portions are provided for accommodating casing sections of the exhaust gas turbocharger. A recess is formed in the first element and/or in the second element for the reduction of stresses. By means of the recess, in particular if both elements comprise recesses, the stresses which are generated over the circumference of the connection device may be better distributed. This means in other words that an accumulation of the corresponding stress at a certain place is prevented so that at this place a high value of the stress is present, while no or only an insignificantly high stress, respectively, is present at another place.

The result is an improved stability during operation of the exhaust gas turbocharger, because the deformation which occurs in particular under varying operating temperatures of the exhaust gas turbocharger is considerably reduced due to the improved stress distribution.

In particular, the recess is formed in a region of the corresponding element, which exhibits high tensile and compressive stresses. Although a cross-section of the connection device is reduced in the region of the recess, the resulting circumferential force is, however, better distributed in the entire connection device so that an accumulation of tensile and compressive stresses is reduced.

In particular, three recesses in the supporting portion have proven advantageous. The reason for this is that the essentially bent supporting portion at the end regions of the element, in particular, is transferred into the respective end region by means of an extreme change in direction of an extension of the element. In this way, almost rectangular contact regions of the end regions with the supporting portion are obtained. These contact regions are subjected to high tensile and compressive stresses. In order to be able, in particular, to reduce them, one recess each is to be arranged in the supporting portion near the contact regions or the end regions of the element, respectively. Furthermore, a recess is to be formed in the region of the supporting portion in the region of the supporting portion which first comes into contact with the casing sections to be accommodated, in particular with their portion collars formed at flange surfaces, because this region when making the firm connection with the exhaust gas turbocharger is subjected to high tensile stresses. Thus, it is advantageous to provide at least three recesses in the supporting portion.

In a further embodiment, the recess is formed in a band of the supporting portion. Thereby, the strength of the supporting portion is maintained while a band cross-section is simultaneously reduced. Preferably, the elements are profiled, comprising a U-shaped cross-section profile. The term U-shaped cross-section profile also includes a V-shaped cross-section profile with a specially adjusted angle between profile flanks of the cross-section profile. Thereby, an improved overall elasticity of the connection device may be achieved which leads to an improved relative adaptation of the connection device to the casing sections to be connected. During tightening, in other words, during clamping of the connection device, bending stresses originate at flanges of the bearing and turbine casing through the applied axial force at the circumference of the connection device. These bending stresses exhibit a maximum in the region of the end portions, in particular at bent regions. The recesses lead to a reduction in stiffness at these places and reduce the stress peaks in the connection device and in the casings.

In order to obtain an adequate section modulus of the element comprising the recess, the recess exhibits a maximum width and a corresponding optimized shape, wherein the maximum width has a value which is not greater than that of a width of the band. The optimized shape is adjusted to the distributed axial force component to be introduced at the circumference.

In a further embodiment of the connection device, the recess is formed mainly rounded, whereby stress cracking due to sharp corners and/or sharp edges of the recess may be excluded.

The second aspect relates to an exhaust gas turbocharger with a first casing section which may in particular be flown through by hot exhaust gas and a second casing section, wherein the first casing section and the second casing section are connected with each other by means of a connection device. The connection device is configured as described.

During operation of the exhaust gas turbocharger, the casing sections exhibit a thermal expansion due to high exhaust gas temperatures. In order to allow this thermal expansion without significantly affecting an efficiency of the exhaust gas turbocharger, the connection device is configured as described. This results in a safe connection between the casing sections and thus in a reduction or elimination of leakage of harmful substances.

Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments as well as from the drawing. The above features and feature combinations mentioned in the description as well as the features and feature combinations in the following description of the figures and/or shown in the figures alone are not only applicable in the indicated combination but also in other combinations or alone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a connection device for an exhaust gas turbocharger.

FIG. 2 shows a cross-section of the connection device according to FIG. 1.

FIG. 3 shows a plan view of the connection device according to FIG. 1.

FIG. 4 shows in a plan view a cutout of the connection device in a first alternative exemplary embodiment.

FIG. 5 shows in a plan view a cutout of the connection device in a second alternative exemplary embodiment.

FIG. 6 shows in a plan view a cutout of the connection device in a third alternative exemplary embodiment.

DETAILED DESCRIPTION

An exhaust gas turbocharger (not shown in detail) comprises a first casing section as a flow-through exhaust gas guide portion which during operation of the exhaust gas turbocharger is flown through by a fluid, generally by exhaust gas. The exhaust gas is generally, but not necessarily, a combustion product of a combustion engine (not shown in detail).

A second casing section, which is formed as a bearing portion and serves to support a rotor assembly (not shown in detail) is associated with the exhaust gas turbocharger. The bearing portion is positioned between a flow-through air guide portion (not shown in detail) of the exhaust gas turbocharger and the exhaust gas guide portion.

The rotor assembly (not shown in detail) comprises a compressor wheel (not shown in detail) and a turbine wheel (not shown in detail), which are connected non-rotatably with each other via a shaft (not shown in detail). The compressor wheel is arranged in a compressor wheel chamber (not shown in detail) of the air guide portion to take in generally fresh air. The turbine wheel (not shown in detail) is rotatably accommodated in a wheel chamber (not shown in detail) of the exhaust gas guide portion.

During operation of the exhaust gas turbocharger, the turbine wheel is subjected to the exhaust gas flowing through the exhaust gas guide portion and driven by it so that it may perform a rotary movement. This rotary movement may be transferred to the compressor wheel via the shaft, which thereby simultaneously to the rotary movement of the turbine wheel may perform a rotary movement. By means of the compressor wheel and its rotary movement, fresh air is taken in which is compressed in the air guide portion.

The exhaust gas guide portion comprises a first flange surface at its end facing the bearing portion. A second flange surface of the bearing portion is formed opposite this first flange surface, wherein the two flange surfaces are formed mainly complementary.

The two flange surfaces are formed to extend both radially as well as in the circumferential direction relative to a longitudinal axis of the exhaust gas turbocharger, which corresponds to an axis of rotation of the turbine wheel. The exhaust gas guide portion comprises a first portion collar opposite the bearing portion, which is associated with an axially adjacent second portion collar of the bearing portion. The first flange surface and the second flange surface extend over the first portion collar and the second portion collar, respectively.

The exhaust gas guide portion and the bearing portion are connected with each other by a connection device 1 in the region of the flange surfaces. The connection device 1 comprises a first element 2 which is mainly bent in the circumferential direction and a second element 3 which is mainly bent in the circumferential direction, which on one end are detachably connected with each other by means of a first connecting element 4 and on the other end are movably connected with each other by means of a second connecting element 5, see FIG. 1 which illustrates the connection device 1 in a perspective view. The connection device 1 is basically formed similar to a pipe clamp connection. In other words, for the connection of the two casing sections a band-shaped connection device 1 is provided which at least partially encompasses the circumference of the first portion collar and the second portion collar in the radial, in the axial and in the circumferential direction.

A first end region 6 of the first element 2 and a second end region 7 of the second element 3 are configured for making a connection by means of the first connecting element 4 which is formed as a screw-nut element and, for this purpose, comprise a first clamping arm 8 and a second clamping arm 9, respectively. In the clamping arms 8, 9 each an opening 10 is formed through which the first connecting element 4, the screw, may be inserted. A head 11 of the first connecting element 4 is formed to rest on the first clamping arm 8. At the element end 12 facing away from the head 11, a clamping disk 13 and a safety element 14, in the present exemplary embodiment in the form of a nut, are arranged, so that the two elements 2, 3 may be clamped together through a preload force of the first connecting element 4.

The first element 2 extends starting from the first clamping arm 8 with a first stop 15, over a first supporting portion 16 to a third end region 17 which comprises a first eye-shaped safety element 18. The second element 3 is formed identically and extends starting from the second clamping arm 9 over a second supporting portion 19 to a second eye-shaped safety element 20 in a fourth end region 21. The second clamping arm 9 comprises a second stop 22 at its second end region 7 which faces away from the second safety element 20.

In order to obtain a relative adaptation of an inner circumference 23 of the connection device 1 to an outer circumference of the portion collars the two elements 2, 3 are made from a profiled material with legs 25 formed between a band 24, which comprises an essentially U-shaped or V-shaped profile. The profile could also be referred to as a trapezoidal profile.

FIG. 2 shows the connection device 1 in a cross-section. The places 26 marked by an arrow identify places where tensile and compressive stresses occur during operation, wherein the places 26, in particular in the third end region 17 and in the fourth end region 21, are places with heavy material reshaping.

For reducing these tensile and compressive stresses, the first supporting portion 16 and the second supporting portion 19 comprise recesses 27. The recesses 27 are formed near the places 26, wherein also a portion region 28 of the supporting portions 16, 19, which in particular during installation is subjected to tensile stress, comprises recesses 27. In the present exemplary embodiment the recess 27 formed in the portion region 28 is arranged centrally between the two recesses in the region of place 26. This means that the element 2; 3 preferably comprises three recesses 27.

Ideally, the places of the tensile and compressive stresses are determined simulatively by means of computational programs, so that the positioning of the recesses 27 brings about a reduction or elimination of the compressive and tensile stresses.

FIGS. 4 to 6 show different shapes of the recesses 27. The choice of a suitable shape of the recess 27 depends on the occurring stresses or the stresses to be expected as well as on the selected material of the elements 2, 3. Another dependency is inherent in the constructive design of the connecting elements 4, 5.

As may be seen in particular in FIG. 3, in a plan view of the connection device 1, the selected shape of the recess 27 here is an elongated hole. Preferably, sharp edges of the recess 27 are to be avoided, because these may cause cracking.

The recesses 27 are formed in such a manner that they completely penetrate the thickness D of the band 24. In order to avoid a reduction in strength of the supporting portions 16, 19, the recesses 27 are portionwise formed at these. Preferably, they are formed to be symmetrically to a band center 29, wherein their maximum width Bmax does not exceed half a band width B. Exceeding half the band width B could lead to weakening, i.e. to a reduction of a section modulus of a cross-section comprising the recess 27 of the corresponding supporting portion 16; 19, which might in particular result in an expansion and thus loosening of the connection device 1 due to increased temperatures.

When positioning the recesses 27, the arrangement of the connection device 1 relative to the casing sections has also to be taken into consideration. A more pronounced thermal expansion is to be expected on the side facing the exhaust gas guide portion of the connection device 1, compared to the side facing the bearing portion of the connection device 1. 

1.-8. (canceled)
 9. A connection device for an exhaust gas turbocharger, comprising: an essentially bent first element (2); and an essentially bent second element (3), wherein the first element (2) and the second element (3) are detachably connected with each other in a first end region (6) or in a second end region (7), respectively, and are movably connected with each other in a third end region (17) or in a fourth end region (21), respectively, and wherein a first supporting portion (16) extends between the first end region (6) and the third end region (17) and a second supporting portion (19) extends between the second end region (7) and the fourth end region (21), and wherein the supporting portions (16, 19) are provided for accommodating casing sections of the exhaust gas turbocharger, and wherein the connection device (1) comprises a recess (27) which is formed in the element (2; 3) for the reduction of stresses, and wherein the recess (27) is formed like an elongated hole, having a width (B) which is smaller than a length of the recess, which extends over the circumference of the element (2, 3).
 10. The connection device according to claim 9, wherein the recess (27) is formed in the supporting portion (16; 19).
 11. The connection device according to claim 9, wherein the recess (27) is formed in a region which is subjected to high tensile and compressive stresses.
 12. The connection device according to claim 9, wherein the supporting portion (16; 19) comprises three recesses (27).
 13. The connection device according to claim 9, wherein the recess (27) is formed in a band (24) of the supporting portion (16; 19).
 14. The connection device according to claim 13, wherein the recess (27) comprises a maximum width (Bmax) which exhibits a value which is not greater than that of a width (B) of the band (24).
 15. The connection device according to claim 9, wherein the recess (27) is formed mainly rounded.
 16. An exhaust gas turbocharger, comprising a first casing section and a second casing section, wherein the first casing section and the second casing section are connected with each other by the connection device as in claim
 9. 